Numerous oculometers or eye-trackers exist in the patent literature. While there exist several methods for following the movements of the eye, such as tightly fitting contact lenses and measurement of minute voltages generated in the region of the eye, the most satisfactory methods available have depended upon the use of radiant energy reflected from the eye. Such reflection dependent methods are either visible light, ultraviolet or infrared radiation and function on the basis of the difference in reflectivity of various portions of the eye. U.S. Pat. No. 3,462,604 shows an example of such an oculometer. The difficulties which are present in the typical reflection oculometer center on the complexity and the lack of sensitivity of the sensing system. An apparatus based on U.S. Pat. No. 3,462,604 typically contains a light source of approximately 100 watts, most of which is lost in heat and other unwanted radiation. Much of the energy is lost in passing through a multiplicity of filters and lenses and other optics before the radiation reaches the eye.
A further difficulty is encountered in the presently used image sensing system. Typically the image of the eye is projected upon the face of a vidicon tube being used in a conventional TV camera. Such a system uses the typical scanning circuitry associated with such a camera and then uses a converter to change the analog information furnished by the camera to digital information which may be used, with complex algorithms, by a computer to produce the analysis of eye-direction information. This method requires the processing of a vast amount of data and also requires a time lag during the scanning operation which may cause the loss of valuable information.
Limitations in sensitivity of such devices as camera tubes also severly limit the eye space which may be monitored. The typical system yields a monitored space of only about one cubic inch. The present method of overcoming the limitation is by the use of servo-controlled mirrors or lenses to follow the eye, as is shown in U.S. Pat. No. 3,462,604 and U.S. Pat. No. 3,804,496. These methods add even greater complexity to the problem of data reduction and furthermore add possibilities of error.